There is currently a strong trend toward downsizing existing structures and fabricating smaller structures. This process is commonly referred to as microfabrication. One area in which microfabrication has had a sizeable impact is in the microelectronic area. In particular, the downsizing of microelectronic structures has generally allowed the structures to be less expensive, have higher performance, exhibit reduced power consumption, and contain more components for a given dimension. Although microfabrication has been widely active in the electronics industry, it has also been applied to other applications such as biotechnology, optics, mechanical systems, sensing devices, and reactors.
One method employed in the microfabrication process is imprint lithography as an alternative to photolithography techniques. Imprint lithography is typically utilized to pattern thin films on a substrate material with high resolution. The thin films patterned can be dielectrics, semiconductors, metals or organics and can be patterned as thin films or individual layers. Imprint lithography is particularly useful for patterning devices in a roll-to roll environment since imprint lithography is not as sensitive to planarity as photolithography. Additionally, imprint lithography has a higher throughput, can handle wider substrates and does not require step and repeat processing.
Previous methods of layer thickness measurements during etching used in typical photolithography techniques include optical interference, optical reflectivity, residual gas analysis (RGA), and ultrasound. In typical photolithography, most etching steps are terminated by using the large differential etch rates between various materials so careful control of etch rates and depths is often not required. However, these previous methods typically have difficulty measuring thin layers (e.g., less than 100 nm) which occur commonly as residual layer thicknesses.
In the case of imprint lithography, the etch rate can depend on the lateral shape of the layer and is uniform across the sample. These factors preclude the use of special test structures. Also, because the various layer thicknesses are laterally close to each other for most structures, it is desirable that the thickness measurement have high lateral spatial resolution for the various levels. The multilevel nature of imprint lithography etching also makes the use of RGA to detect lay removal for endpoint detection rather difficult because the different layer thicknesses contribute to the signal. Moreover, in the case of roll-to-roll processing, the typical endpoint detection is inadequate because the sample has all thicknesses present at the same time in steady state. Hence, the onset of a new signal indicating etching of a new layer is much less pronounced.
Accordingly, what is needed is a manner of remote real time layer thickness monitoring for etching.